For self-assessment questions, with exercises and discussions, just click on the correct topic at Biology GCSE & IGCSE Question Bank. A powerpoint can be downloaded from the same site here. The s-cool revision sitelets you revise the topic, summarizes the topic & tests you on it. Skooolgives you a lesson, including progress questions, for each Biology topic but you’ll need sound on for it. GCSE Bitesize has revision pages (that take you through the topic), a test and an activity.